Conventionally, it has been a common practice to form an electromagnetic wave-shielded room for the purpose of shielding an externally intruding unnecessary electromagnetic wave and preventing leakage of an internally generated electromagnetic wave to the outside. An electromagnetic wave-shielded room is formed with an intended section being surrounded with a plate member of a conductive material and the plate member being grounded. When power is to be transmitted from one to the other of the inside and the outside of an electromagnetic wave-shielded room, a through hole is formed in a plate member for blocking the propagation of an electromagnetic wave, and a power transmission device penetrating through the through hole is provided, thereby allowing power to be transmitted through the plate member forming the electromagnetic wave-shielded room.
When an electromagnetic wave-shielded room is provided with a power transmission device in the above manner, in the event of leakage of a radio wave by way of the through hole or leakage of a radio wave transmitted through the shaft, the shielding performance against an electromagnetic wave would be degraded. In particular, the higher frequency an electromagnetic wave has, the more likely the electromagnetic wave is to be transmitted by way of the surface of the shaft due to the skin effect. In order to achieve improved shielding performance against an electromagnetic wave of a high frequency, it is necessary to block an electromagnetic wave leaking through the shaft surface. To that end, a technology has been proposed in which a through hole formed in a plate member of a conductive material is penetrated thorough by a sleeve made of metal so that leakage of an electromagnetic wave by way of the through hole is suppressed, and in which a direct-coupling shaft of an insulating material is inserted into the sleeve so that leakage of an electromagnetic wave by way of the shaft is also suppressed (for example, see Japanese Patent Laying-Open No. 8-326340 (Patent Document 1)).    Patent Document 1: Japanese Patent Laying-Open No. 8-326340